Surgical fasteners of two part construction are quite well-known in the art. Typically, these surgical fasteners which contain two parts are formed from one or more absorbable materials. The fastener itself contains a tissue piercing portion, i.e., a staple or fastener, and a receiving portion for the staple or fastener. The tissue to be joined may be generally two layers of tissue which are held between the fastener and receiver or may be tissue to be ligated. For cases where ligation occurs, it is generally the objective of the fastener to generate a compressive force on the tissue, which will prevent the flow of blood through the tissue. The absorbable nature of the fastener allows the fastener to be absorbed into the body after the separated tissue has adhered, so that there are no extraneous materials contained in the body after healing.
Yet, for all the tissue fasteners which are formed from a two piece construction, it has been observed that generally these fasteners maintain the tissue so that it is compressed between the fastener and the receiver in a fixed gap. That is, a portion of the tissue forms a layer which is below the fastener layer and above the receiver layer. The tissue contained between the fastener and receiver therefore undergoes compression due to the fixed gap which is present between the fastener and receiver and the resilient nature of the material that is being compressed. When traditional fixed-gap fasteners have been applied to tissues, this compressive force can significantly decrease over time due to the visco-elastic nature of the tissue. This can potentially lead to postoperative bleeding of the tissue which is not desirable. Additionally, the tissue will not be adequately compressed in traditional fastener/receivers if the fastener/receiver does not have the proper gap size for the type of tissue in question.
It is perceived that it is desirable to have tissue compression at a number of various places along the tissue which is to be ligated or joined. In traditional fastener/receiver systems this is accomplished by an alternating staggered line of individual fasteners with one or more receivers. This method of compression can be effective because it allows for capillary flow of blood at the fastener location which prevents necrosis of the tissue. However, it also requires a plurality of fasteners, each of which must penetrate the tissue. It has been observed that this multiplicity of penetrations can lead to localized bleeding at the locations of tissue penetration. The multiplicity of fasteners is also undesirable from a manufacturing viewpoint due to the number as well as size of the components involved. It is therefore desirable to create an alternative method for tissue compression which minimizes the number of penetrating fasteners.
Also, with such fasteners made from absorbable products, there has only been one way in which to adjust the gap or spacing between the tissue fastener and the staple receiver. This occurs via a ratcheting mechanism placed on the tissue piercing prongs of the fastener and creates a fixed gap between bottom of staple and top of receiver. When the piercing prongs are engaged in holes formed on the receiver, the ratcheting mechanism enables the device to be gradually closed to a varying thickness. Therefore, the final gap is reliant upon the instrument causing the fastener to ratchet to a determined position. The complexity associated with this increases the cost of the instrument and makes reliable ratcheting of the fasteners difficult, if not impossible. To simplify the instrument it would be desirable for the fastener to have the capacity to adjust automatically to the tissue.
By having the self-adjustment determined by the fastener and not the instrument, compression of adjacent tissues which are very different in thickness can be accomplished with a single self-adjusting device as opposed to two devices with different gap heights. In addition, the compressive force can be maintained even when the tissue loses its resiliency over time. Thus optimal tissue compression can be maintained by having the compression adjusted by the device itself, and not the instrument.